1. Field of the Disclosure
The present disclosure relates generally to a fluid ejection device for inkjet printers, and more particularly, to a fluid ejection device that provides a narrow print zone in the media transport direction for better print quality when multiple devices are formed end-to-end in an array.
2. Description of the Related Art
Typically, a printer, such as an inkjet printer, includes a page wide fluid ejection device (printhead) that has an array of narrow ejection chip units (e.g. heater chips). In general, the width of such narrow ejection chip units is less than about two millimeters (mm). Further, each ejection chip unit of the page wide fluid ejection device includes about four to five fluid (ink) channels for fluids (inks) of colors, such as Cyan, Magenta, Yellow, and blacK (CMYK). FIG. 1 depicts a three dimensional exploded view of a typical narrow ejection chip unit, such as an ejection chip unit 100, of a typical page wide fluid ejection device. The ejection chip unit 100 includes a first ultra thin layer 102 having a plurality of fluid vias 104 to feed firing chambers (not shown) of the fluid ejection device for fluid ejection. The plurality of fluid vias 104 is hereinafter referred to as ‘vias 104’. Each via of the vias 104 is connected to a corresponding firing chamber (not shown) of the fluid ejection device such that each firing chamber is fed by a single via of the vias 104.
The ejection chip unit 100 further includes a substrate layer 106 having a plurality of fluid (ink) channels 108, across the length of the ejection chip unit 100. For the purpose of this description, the ejection chip unit 100 includes four fluid channels 108 that are adapted to carry the fluids (inks) of cyan color, magenta color, yellow color and black color, respectively. The fluid channels 108 are configured beneath the vias 104 on the substrate layer 106. Each fluid channel of the fluid channels 108 is fluidly coupled with at least one corresponding via of the vias 104. The term, “at least one corresponding via” as to used herein refers to one or more vias of the vias 104 that are aligned with a respective fluid channel of the fluid channels 108 and may carry a fluid ink of the same color as carried by the respective fluid channel.
Furthermore, the ejection chip unit 100 includes a second ultra thin layer 110 having a plurality of ports 112 configured beneath the fluid channels 108. The plurality of ports 112 is hereinafter referred to as ‘ports 112’. At least one port of the ports 112 may be fluidly coupled with a corresponding fluid channel of the fluid channels 108. The term, “a corresponding fluid channel” as used herein refers to a fluid channel of the fluid channels 108 that may be aligned with respective at least one port of the ports 112 and may carry a fluid of the same color as carried by the respective at least one port. As depicted in FIG. 1, the fluid channels 108 are sandwiched between the first ultra thin layer 102 and the second ultra thin layer 110. Specifically, the first ultra thin layer 102, the substrate layer 106, and the second ultra thin layer 110 may be formed from different wafers that are bonded to each other to constitute a wafer stack and to configure the ejection chip unit 100.
It is to be observed that the spacing (seal width) between the two adjacent fluid channels of the fluid channels 108 is as narrow as 0.1 mm, as depicted by distance ‘D1’ in FIG. 2 that illustrates a side cross-sectional partial view of a fluid ejection device 10 employing the ejection chip unit 100 shown with the two adjacent fluid channels of the fluid channels 108 of FIG. 1, and attached with a flow feature layer 12 and a nozzle plate 14. Such narrow seal width averts the use of adhesive bonding that requires wide spacing for the dispensing of an adhesive to connect the ejection chip unit 100 to a substrate (not shown), which is further attached to one or more fluid reservoirs (not shown). Accordingly, to achieve such narrow seal width, direct silicon bonding techniques, such as fusion bonding, anodic bonding and the like, may be employed. Thereafter, patterning of the ports 112, may be carried out, wherein the spacing between nearest ports may be maintained at about 0.2-0.8 mm, which is suitable for low temperature adhesive bonding. Also, fabrication of a photo-imagable nozzle plate (PINP) requires low temperature post processes.
Further, to minimize fluidic resistance within the fluidic ejection device 10, the thickness of the first ultra thin layer 102 and the second ultra thin layer 110 is required to be kept minimum, typically around 30 microns (0.03 mm). Therefore, to achieve such minimum thickness, wafer grinding is required from both sides of the wafer stack formed by bonding the different wafers used to form the first ultra thin layer 102, the substrate layer 106, and the second ultra thin layer 110 of FIG. 1. However, the embedded fluid channels 108 of the substrate layer 106 greatly challenge the grinding of the bonded wafers to achieve such narrow thickness without any cracks. Further, it was observed that a crack-free grinding process may only assist in achieving a minimum of about 0.1 mm thick membrane (i.e., the first ultra thin layer 102) over the fluid channels 108 that is still far away from the expected 0.03 mm thickness for acceptable fluidic resistance in order to provide a narrow print zone for better print quality.
Accordingly, there persists a need for an effective and efficient fluid ejection device and a method for fabricating the fluid ejection device, for providing a narrow print zone for better print quality.